MSH, or Melanocyte-Stimulating Hormone, is produced by the intermediate lobe of the pituitary and stimulates the production and subsequent release of melanin from specialized cells called melanocytes in skin and hair. Melanins are natural pigments that are produced by the oxidation of the amino acid tyrosine and are responsible for the brown, black, red, and pink colorations of the body.
An increased production of MSH is a cause of hyperpigmentation or darker skin tones. MSH is also influenced by estrogens. During pregnancy, for example, excess production of estrogen often causes increased production and release of melanin and a darkening of the skin.
MSH and Adrenocorticotropic hormone (ACTH) share the same precursor molecule, called Pro-opiomelanocortin (POMC), produced by the corticotroph cells of the anterior pituitary. People with Cushing Disease, associated with an increased production of ACTH, are known to have hyper-pigmented areas of skin.
